1. Field of the Invention
The present invention relates to optical drivers and more particularly to a method and apparatus for optical axis adjustment of optical driver with improved characteristics.
2. Description of the Related Art
Optical drivers such as CD-ROMs have been widely used as high-capacity forms of storage. Optical drivers are indispensable in modem computers. It is known that a CD-ROM drive acts to read data from a CD-ROM for transmitting the same to a computer for processing. A conventional optical driver is shown in FIG. 1 including a spindle module 11, a read/write device 12, a control circuit device 13, and a pair of adjustment rods 14. The read/write device 12 is slidingly supported by the adjustment rods 14 such that the read/write device 12 may reciprocally move in a lengthwise direction of the adjustment rods 14. This defines a read plane. An optical storage medium (e.g., disc) 15 is rotatably supported on the spindle module 11. This defines a rotation plane. The read/write device 12 acts to continuously emit an incident light signal to the disc. Such incident light signal is then reflected by the disc to form a reflected light signal which is in turn received by the read/write device 12. Next, the reflected light signal is converted by the read/write device 12 to generate an output reflected voltage signal (a voltage signal corresponding to the reflected light signal). The traveling path of incident light signal, i.e., from the read/write device 12 to disc 15 on the rotation plane, is called an optical axis. The optical axis is required to be perpendicular to the rotation plane. That is, incident angle Q is zero. Note that incident angle Q is defined as the angle of incident light signal 21 with respect to the normal line 23 of the rotation plane 22 of the disc, as shown in FIG. 2. The control circuit device 13 acts to output a rotation control signal to the spindle module 11 for enabling spindle module 11 to rotate. The control circuit device 13 also acts to output a read/write control signal to the read/write device 12 for activating read/write device 12 to emit an incident light signal or receive the incident light signal.
Referring to FIG. 3, a plurality of adjustment devices 31 are provided on the underside of spindle module 11 for adjusting the optical axis to be perpendicular to the rotation plane. In adjusting the adjustment devices 31, the spindle module 11 is activated to slant. As such, the rotation plane of the disc is also slanted to change the incident angle to be about or equal to zero. Referring to FIG. 4, the incident angle adjustment technique of the optical driver in FIG. 1 is illustrated. The reflected light signal from the disc is received by the read/write device 12. Next, the reflected light signal is converted by the read/write device 12 to generate a reflected voltage signal. The reflected voltage signal is then sent to an error detector 41 through the control circuit device 13. A light error signal (if any) is then generated and shown. As such, an inspection person may visually adjust the light error signal by using a plurality of adjustment rods 42 to rotate the adjustment devices 31. Preferably, the value of the adjusted light error signal is a minimum. In this manner, the optical axis may be adjusted to be perpendicular to the disc. The above light error signal may be represented by means of an average standard deviation for measuring the standard deviation in the reflected voltage signals between a predetermined period of time of the signal and a standard period of time set by the error detector. The light error signal may be represented by the equation below.             (              light        ⁢                  xe2x80x83                ⁢        error        ⁢                  xe2x80x83                ⁢        signal            )        2    =                    ∑                  i          =          1                w            ⁢              xe2x80x83            ⁢                        (                      Xi            -                          x              xe2x80x2                                )                2                    (              n        -        1            )      
where Xxe2x80x2 is a standard period of time set by the error detector and Xi is the measured value of the reflected voltage signal outputted by the read/write device 12 in the 20 predetermined period of time. For example, as Xxe2x80x2 is 3*T and then Xi is 2.8*T or 3.1 *T during a predetermined period of time equal to 3*xe2x80x98Ixe2x80x99. Further, n is the number of samples and T is a predetermined period of time. However, the light error signal is not a constant. It is susceptible to interference of other factors. For example, the factors include the quality of disc, contamination, noises, and the like. As such, the variation is relatively large. This adversely affects the adjustment of optical axis. Referring to FIG. 5, a chart is shown for illustrating the variation of light error signals due to the interference of other factors versus a plurality of different incident angles. As shown, the width of curve is the amplitude of vibration of the light error signal. It is seen that the light error signal is varied significantly even when the incident angle is fixed. This not only adversely affects the adjustment of optical axis, but also prolongs the adjustment time and decreases yield. Moreover, the cost of an error detector is very high. As such, it is not economical to use the error detector as an adjustment device for adjusting the optical axis of the CD-ROM drive only.
It is an object of the present invention to provide a method for optical axis adjustment of an optical driver for decreasing the interference of other external factors and providing a reliable sensitive determination with respect to the variation of incident angle for facilitating the inspection person""s observation and quickly precisely adjusting the incident angle to an optimum.
It is another object of the present invention to provide an apparatus for optical axis adjustment of an optical driver for precisely adjusting the incident angle to an optimum, thereby saving cost and increasing yield.